Photo-injection of high potential holes into Cu5Ta11O30 nanoparticles by porphyrin dyes

I. SULLIVAN, C. BROWN, M. J. LLANSOLA-PORTOLES, G. KODIS, T. A. MOORE, D. GUST, A. MOORE, P. MAGGARD; M GERVALDO

Thirty-Seventh DOE Solar Photochemistry P.I. Meeting

Congreso; Thirty-Seventh DOE Solar Photochemistry P.I. Meeting; 2015

Excited-state hole injection (Fig. 1a, step 2) into the valence band of Cu5Ta11O30 nanoparticles (NP-Cu5Ta11O30) was investigated through sensitization with zinc porphyrin dyes using excitation at 515 nm (Fig. 1a, step 1). The Cu5Ta11O30 nanoparticles were prepared by a flux-mediated synthesis andfound to have an average particle size of ~10?15 nm by dynamic light scattering and high resolution transmission electron microscopy. The zinc 4-(10,15,20-tris(4-pyridinyl)-porphin-5-yl)phenylphosphonic acid (Fig. 2 D1) and its analogin which the pyridine groups are methylated (Fig. 2 D2) were synthesized and found to have excited state reduction potentials appropriate for p-type dye sensitization of the nanoparticles. Electron injection from the dye excited singlet state to the conduction band (CB) of the nanoparticle was not observed and is thermodynamically precluded because the CB is more than 1 V more negative (< -1.5V vs NHE) than the excited state oxidation potential of the dye. The dye-sensitized NPCu5Ta11O30 exhibited fluorescence quenching consistent withelectron transfer from the NP-Cu5Ta11O30 to the excited singlet state of the dye (Fig. 1a, step 2 shown as h+ injection); forward and recombination (Fig. 1a, step 3 shown as h+ transfer) rates were obtained by transient absorption measurements. Hole injection times of 8 ps and